Once you've installed the app, swipe to bring down Notification Center, then tap Today if it's not already selected. Scroll down to the bottom and tap Edit to access the list of available widgets. You should see eight new ones, all of them identifiable by the bright orange Wdgts icon. (Here's a more complete tutorial on using widgets in iOS 8 if you're not familiar with the process.)

The free version of the app comes with five:

Calculator

Calendar (month view)

Currency Converter

Photo Frame

Time Zones

You can also test-drive any of the three Premium widgets:

Battery Gauge

Memory/Storage Gauge

Network Monitor

However, unless you pay 99 cents via in-app purchase (£0.69, AU$1.29), these three will appear in your widgets list only one time -- effectively letting you try before you buy.